The field of the present invention relates generally to vacuum rolls, and more particularly to vacuum rolls for holding, controlling, transferring, folding, winding or otherwise handling flexible materials.
One known type of vacuum roll includes a rotatable outer cylindrical wall defining an interior space and a plurality of apertures extending through the cylindrical wall and in fluid communication with the interior space. One or more stationary vacuum manifolds are disposed within the interior space and operatively connected to a vacuum source. Vacuum can be selectively applied to one or more of the vacuum manifolds by operating the vacuum source.
In another known type of vacuum roll, each of the vacuum manifolds is rotatable with the outer cylindrical wall. For example, a first plurality of apertures in the cylindrical wall is in fluid communication with one of the manifolds and a second plurality of apertures in the cylindrical wall is in fluid communication with another one of the manifolds. Vacuum can be selectively applied to the first plurality of apertures and/or the second plurality of apertures at any location about the rotation of the outer cylinder by regulating the vacuum applied by the vacuum source to the respective manifold. Regulation of the vacuum source is most commonly performed using one or more valves (e.g., solenoid valves). In other words, the vacuum applied to each of the manifolds can be selectively turned “on” and “off” by opening and closing a valve.
However, there remains a need for a vacuum roll capable of changing its vacuum profile even while the vacuum roll is handling a material at a high line speed.